Characterization of Lithium Storage in TiO2(B) by 6Li-NMR and X-Ray Diffraction Analysis

Abstract

Lithium storage in TiO2(B) was investigated by 6Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR) and ex-situ X-ray diffraction (XRD) analysis combined with the entropy (ΔS) and galvanostatic intermittent titration technique (GITT) measurements. Lithium storage sites in TiO2(B) were characterized to be separated from four bands assigned to different lithium storage sites. Band A at 0 ppm vs. LiCl in the 6Li NMR spectra and ΔS measurements indicated that ionic lithium was stored at surface domain of LixTiO2(B) up to x = 0.18. Band B at 2.5 ppm significantly increased with lithium insertion in the region for 0.25 < x < 0.5, which indicated that lithium was mainly inserted into the site lying between bridging oxygens in LixTiO2(B). Additionally, the site on the lithium diffusion path along b-axis was also occupied by a small amount of lithium. The stepwise change of OCV and ΔS at around x = 0.45 indicated that lithium was inserted at the site in TiO2 layer in LixTiO2(B). In the region for x > 0.75, Band D was observed at more positive chemical shift than Band B. The lithium at the site distorted the local structure of LixTiO2(B), which leads to decrease of the lithium diffusivity in LixTiO2(B).